Complementary metal oxide semiconductor replacement gate high-k metal gate devices with work function adjustments

ABSTRACT

An electrical device that includes a p-type semiconductor device having a p-type work function gate structure including a first high-k gate dielectric, a first metal containing buffer layer, a first titanium nitride layer having a first thickness present on the metal containing buffer layer, and a first gate conductor contact. A mid gap semiconductor device having a mid gap gate structure including a second high-k gate dielectric, a second metal containing buffer layer, a second titanium nitride layer having a second thickness that is less than the first thickness present, and a second gate conductor contact. An n-type semiconductor device having an n-type work function gate structure including a third high-k gate dielectric present on a channel region of the n-type semiconductor device, a third metal containing buffer layer on the third high-k gate dielectric and a third gate conductor fill present atop the third metal containing buffer layer.

FIELD OF THE INVENTION

The present disclosure relates generally to semiconductor devices, andmore particularly to work function modifications in semiconductordevices.

BACKGROUND

Field effect transistors (FETs) are widely used in the electronicsindustry for switching, amplification, filtering and other tasks relatedto both analog and digital electrical signals. Most common among theseare metal oxide semiconductor field effect transistors (MOSFET or MOS),in which a gate structure is energized to create an electric field in anunderlying channel region of a semiconductor body, by which electronsare allowed to travel through the channel between a source region and adrain region of the semiconductor body. Complementary MOS (CMOS) deviceshave become widely used in the semiconductor industry, wherein bothn-type and p-type (NMOS and PMOS) transistors are used to fabricatelogic and circuitry.

Continuing trends in semiconductor device manufacturing include areduction in electrical device feature size (scaling), as well asimprovements in device performance in terms of device switching speedand power consumption. Some examples of methods to improve deviceswitching include adjusting the work function of the materials in thegate structure.

SUMMARY

In one aspect of the present disclosure, an electrical device isprovided that includes a semiconductor substrate having an n-typeregion, a p-type region and a mid gap region. A p-type semiconductordevice is present in the p-type region having a p-type work functiongate structure comprised of a first high-k gate dielectric, a firstmetal containing buffer layer present on the first high-k gatedielectric, a first titanium nitride layer having a first thicknesspresent on the metal containing buffer layer, and a first gate conductorcontact present on the first titanium nitride layer. A mid gapsemiconductor device is present in the mid gap region of thesemiconductor substrate having a mid gap gate structure comprised of asecond high-k gate dielectric, a second metal containing buffer layerpresent on the second high-k gate dielectric, a second titanium nitridelayer having a second thickness that is less than the first thicknesspresent on the second metal containing buffer layer, and a second gateconductor contact present on the second titanium nitride layer. Ann-type semiconductor device is present in the n-type region having ann-type work function gate structure comprised of a third high-k gatedielectric present on a channel region of the n-type semiconductordevice, a third metal containing buffer layer on the third high-k gatedielectric and a third gate conductor fill present atop the third metalcontaining buffer layer.

In one embodiment of the present disclosure, an electrical device isprovided that includes a semiconductor substrate having an n-typeregion, a p-type region and a mid gap region. A p-type semiconductordevice is present in the p-type region having a p-type work functiongate structure comprised of a first high-k gate dielectric, a firstmetal containing buffer layer present on the first high-k gatedielectric, a first titanium nitride layer having a first thicknesspresent on the metal containing buffer layer, and a first gate conductorcontact present on the first titanium nitride layer. A mid gapsemiconductor device is present in the mid gap region of thesemiconductor substrate having a mid gap gate structure comprised of asecond high-k gate dielectric, a second metal containing buffer layerpresent on the second high-k gate dielectric, a second titanium nitridelayer having a second thickness that is less than the first thicknesspresent on the second metal containing buffer layer, and a second gateconductor contact present on the second titanium nitride layer. Ann-type semiconductor device is present in the n-type region having ann-type work function gate structure comprised of a third high-k gatedielectric present on a channel region of the n-type semiconductordevice, a third metal containing buffer layer on the third high-k gatedielectric, a third titanium nitride layer present on the third metalcontaining buffer layer having a third thickness less than the secondthickness, and a third gate conductor fill present atop the thirdtitanium nitride layer.

In another aspect, a method of forming a semiconductor device isprovided that includes providing semiconductor substrate having ann-type region, a p-type region and a mid gap region. Forming a p-typesemiconductor device in the p-type region having a p-type work functiongate structure comprised of a first high-k gate dielectric, a firstmetal containing buffer layer present on the first high-k gatedielectric, a first titanium nitride layer having a first thicknesspresent on the metal containing buffer layer, and a first gate conductorcontact present on the first titanium nitride layer. Forming a mid gapsemiconductor device in the mid gap region of the semiconductorsubstrate having a mid gap gate structure comprised of a second high-kgate dielectric, a second metal containing buffer layer present on thesecond high-k gate dielectric, a second titanium nitride layer having asecond thickness that is less than the first thickness present on thesecond metal containing buffer layer, and a second gate conductorcontact present on the second titanium nitride layer. Forming an n-typesemiconductor device in the n-type region having an n-type work functiongate structure comprised of a third high-k gate dielectric present on achannel region of the n-type semiconductor device, a third metalcontaining buffer layer on the third high-k gate dielectric, a thirdtitanium nitride layer present on the third metal containing bufferlayer having a third thickness less than the second thickness, and athird gate conductor fill present atop the third titanium nitride layer.

DESCRIPTION OF THE DRAWINGS

The following detailed description, given by way of example and notintended to limit the invention solely thereto, will best be appreciatedin conjunction with the accompanying drawings, wherein like referencenumerals denote like elements and parts, in which:

FIG. 1A is a side cross-sectional view of an electrical device includingn-type FinFETs, p-type FinFETs and mid gate FinFETs, wherein the gatestructures in at least the p-type FinFETs and mid gate FinFETs include atitanium layer having a thickness selected for adjusting the workfunction of the gate structure, in accordance with one embodiment of thepresent disclosure.

FIG. 1B is a side cross-sectional view of an electrical device includingn-type planar semiconductor devices, p-type planar semiconductor devicesand mid gate planar semiconductor devices, wherein the gate structuresin at least the p-type planar devices and the mid gate planar devicesinclude a titanium layer having a thickness selected for adjusting thework function of the gate structure, in accordance with one embodimentof the present disclosure.

FIG. 2A is a side cross-sectional view (i.e., cross sectional along alength of the fin structure) depicting forming a sacrificial gatestructure on a plurality of fin structures, in which one of the finstructures is for n-type device, one of the fin structures is for ap-type device and one of the fin structures is for a mid gap device inaccordance with one embodiment of the present disclosure.

FIG. 2B is a side cross-sectional view depicting one embodiment of asacrificial gate structure on a plurality of regions of a semiconductorsubstrate for forming planar semiconductor devices, in which one of thesacrificial gate structures is present on a channel region for an n-typedevice, one of the sacrificial gate structures is present on a channelregion for a p-type device and one of the sacrificial gate structure isfor a mid gap device.

FIG. 3A is a side cross-sectional view depicting removing thesacrificial gate structure from the structure depicted in FIG. 2A, andforming a high-k gate dielectric on each of the fin structures for thep-type FinFET, the mid gap FinFET and the n-type FinFET.

FIG. 3B is a side cross-sectional view depicting removing thesacrificial gate structure from the structure depicted in FIG. 2B, andforming a high-k gate dielectric on each of the channel regions for theplanar p-type FET, the planar mid gap FET and the planar n-type FET.

FIG. 4A is a side cross-sectional view forming a gate stack of a metalcontaining buffer layer on the high-k gate dielectric depicted in FIG.3A and a first titanium nitride layer having a first thickness on themetal buffer layer.

FIG. 4B is a side cross-sectional view forming a gate stack of a metalcontaining buffer layer on the high-k gate dielectric depicted in FIG.3B and a first titanium nitride layer having a first thickness on themetal containing buffer layer.

FIG. 5A is a side cross-sectional view depicting forming a block maskover the portion of first titanium nitride that is present on the finstructure for the p-type FinFET that is depicted in FIG. 4A, inaccordance with one embodiment of the present disclosure.

FIG. 5B is a side cross-sectional view depicting forming a block maskover the portion of first titanium nitride that is present over thechannel region for the p-type planar device that is depicted in FIG. 4B,in accordance with one embodiment of the present disclosure.

FIG. 6A is a side cross-sectional view depicting removing the firsttitanium nitride layer from the channel region of the fin structures forthe mid gap device and the n-type device of the structures depicted inFIG. 5A, in accordance with one embodiment of the present disclosure.

FIG. 6B is a side cross-sectional view depicting removing the firsttitanium nitride layer from the channel region of the planar FETs forthe mid gap device and the n-type device of the structures depicted inFIG. 5B, in accordance with one embodiment of the present disclosure.

FIG. 7A is a side cross-sectional view depicting forming a secondtitanium nitride layer having a second thickness that is less than thethickness of the first titanium nitride layer on the channel region ofthe fin structure for the mid gap device, in accordance with oneembodiment of the present disclosure.

FIG. 7B is a side cross-sectional view depicting forming a secondtitanium nitride layer having a second thickness that is less than thethickness of the first titanium nitride layer on the channel region ofthe planar semiconductor device that is a mid gap device, in accordancewith one embodiment of the present disclosure.

DETAILED DESCRIPTION

Detailed embodiments of the methods and structures of the presentdisclosure are described herein; however, it is to be understood thatthe disclosed embodiments are merely illustrative of the disclosedmethods and structures that may be embodied in various forms. Inaddition, each of the examples given in connection with the variousembodiments of the disclosure are intended to be illustrative, and notrestrictive. Further, the figures are not necessarily to scale, somefeatures may be exaggerated to show details of particular components.Therefore, specific structural and functional details disclosed hereinare not to be interpreted as limiting, but merely as a representativebasis for teaching one skilled in the art to variously employ themethods and structures of the present disclosure.

References in the specification to “one embodiment”, “an embodiment”,“an example embodiment”, etc., indicate that the embodiment describedmay include a particular feature, structure, or characteristic, butevery embodiment may not necessarily include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it is submitted that it is within the knowledge of oneskilled in the art to affect such feature, structure, or characteristicin connection with other embodiments whether or not explicitlydescribed. For purposes of the description hereinafter, the terms“upper”, “lower”, “right”, “left”, “vertical”, “horizontal”, “top”,“bottom”, and derivatives thereof shall relate to the invention, as itis oriented in the drawing figures. The terms “overlying”, “atop”,“positioned on” or “positioned atop” means that a first element, such asa first structure, is present on a second element, such as a secondstructure, wherein intervening elements, such as an interface structure,e.g. interface layer, may be present between the first element and thesecond element. The term “direct contact” means that a first element,such as a first structure, and a second element, such as a secondstructure, are connected without any intermediary conducting, insulatingor semiconductor layers at the interface of the two elements.

The present disclosure is relates to forming semiconductor dices, suchas planar semiconductor devices, FinFET semiconductor devices, mid gapsemiconductor devices, p-type semiconductor devices, and n-typesemiconductor devices, in which the work function of the gate structureto the semiconductor devices is adjusted by adjusting the thickness of atitanium nitride layer that is present in the gate structure. As usedherein, “semiconductor device” refers to an intrinsic semiconductormaterial that has been doped, that is, into which a doping agent hasbeen introduced, giving it different electrical properties than theintrinsic semiconductor. Doping involves adding dopant atoms to anintrinsic semiconductor, which changes the electron and hole carrierconcentrations of the intrinsic semiconductor at thermal equilibrium.Dominant carrier concentration in an extrinsic semiconductor determinesthe conductivity type of the semiconductor. In the followingdescription, the semiconductor device is a field effect transistor.

Complementary metal oxide semiconductor (CMOS) is a type ofsemiconductor that use both N-type (negative polarity) and P-type(positive polarity) semiconductor circuits. Typically, since only one ofthe circuit types is on at any given time, CMOS chips require less powerthan chips using just one type of transistor. A “field effecttransistor” is a transistor in which output current, i.e., source-draincurrent, is controlled by the voltage applied to a gate structure. Afield effect transistor typically has three terminals, i.e., a gatestructure, source region and drain region. As used herein, the term“source” is a doped region in the semiconductor device, in whichmajority carriers are flowing into the channel. As used herein, the term“channel” is the region underlying the gate structure and between thesource and drain of a semiconductor device that becomes conductive whenthe semiconductor device is turned on. As used herein, the term “drain”means a doped region in semiconductor device located at the end of thechannel, in which carriers are flowing out of the transistor through thedrain. A “gate structure” means a structure used to control outputcurrent (i.e., flow of carriers in the channel) of a semiconductingdevice through electrical or magnetic fields.

The term “planar” as used to describe a semiconductor deviceorientation, e.g., planar FET, denotes that the direction of chargecarriers from the source region to the drain region of the semiconductordevice is along a plane that is parallel to the upper surface of thesubstrate, wherein a gate structure is present on the upper surface ofthe substrate. In a planar semiconductor device, the gate structure doesnot wrap around the sidewalls of the channel region as in a finstructure.

A FinFET is a field effect transistor in which at least the channelportion of the field effect transistor is present in a fin structure. Asused herein, a “fin structure” refers to a semiconductor material, whichcan be employed as the body of a semiconductor device, in which the gatestructure is positioned around the fin structure such that charge flowsdown the channel on the two sidewalls of the fin structure andoptionally along the top surface of the fin structure.

Although the present disclosure particularly depicts FinFETsemiconductor devices and planar semiconductor devices in the providedillustrations, the present disclosure is not limited to only theseembodiments, as any semiconductor device that includes a gate structurethat may be electrically impacted by work function adjustments issuitable for use with the methods and structures disclosed herein.

The term “work function” is used to describe a gate electrode materialthat determines the threshold voltage of a semiconductor device. Forexample, a work function adjustment effectuates a threshold voltageshift either towards the valence band or conduction band. As usedherein, “threshold voltage” is the lowest attainable gate voltage thatwill turn on a semiconductor device, e.g., transistor, by making thechannel of the device conductive. A “valence band” is the highest rangeof electron energies where electrons are normally present at absolutezero.

The “conduction band” is the lowest lying electron energy band of thedoped material that is not completely filled with electrons.

It has been determined that in some examples of prior semiconductordevices, a variety of work-function (WF) metals are used in order toobtain the desired work-function on nFET and pFET and mid gap devices inreplacement gate integration. However, these work-function metals (WF)alone are not low enough in resistivity and require the use ofadditional fill metals with low resistivity to be deposited on top ofthe work-function metal. In current, designs there are about 4 layers to5 layers of metals being deposited. As the technology is scaled from 32nm node to 22 nm/15 nm nodes, and beyond it will be extremelychallenging to fill the narrow gates with this complicated sandwichstack of metals. Moreover, any solution to the substitution of the 4 or5 layers of work function metals in increasingly scaled gate structuresalso needs to be viable for a complementary metal oxide semiconductor(CMOS) technology with about 300 mV to 400 mV separation between thenFET and pFET gate stack at acceptable leakage specifications.

In some embodiments, the methods and structures that are disclosedherein provide a simplified solution of replacement gate integrationinvolving the presence of one work function metal in combination with abarrier metal thereby providing adequate space for fill metals. In oneembodiment, a deposition process, such as atomic layer deposition (ALD),is used to form the gate structure layers, i.e., work function adjustinglayers, to ensure that uniform and conformal deposition is provided forthe gate structure layers. The methods and structures disclosed hereinprovide a simplified integration strategy for complementary metal oxidesemiconductor (CMOS) technology with a 300 mV to 400 mV separationbetween the different polarity devices, e.g., n-type and p-type devices.Additionally, the methods and structures that are disclosed hereinreduce the number of patterned and etch steps to provide differentialwork functions for the n-type and p-type devices. As will be furtherdiscussed below, the methods and structures disclosed herein employ astack composed of a metal containing buffer layer and a titanium nitridelayer, in which the metal containing buffer layer protects an underlyinghigh-k gate dielectric and adjusting the thickness of the titaniumnitride layer adjusts the work function to obtain target work functionsfor n-type semiconductor devices, p-type semiconductor devices and midgap semiconductor devices.

For example, the titanium nitride layer may be adjusted to have agreatest thickness in the gate structure of the p-type semiconductordevice to provide a p-type work function adjustment, and the titaniumnitride layer may be adjusted to a least thickness in the gate structureof the n-type semiconductor device to provide an n-type work functionadjustment, wherein the titanium nitride layer having the mid gap workfunction for the mid gap structure has a thickness in between thethickness of the titanium nitride layer of the p-type and n-typedevices. As used herein, a “p-type work function” may also be referredto as a high work function, in which the work function is close in valueto the valance band. As used herein, an “n-type work function” may alsobe referred to as a low work function, in which the work function isclose in value to a conduction band. As used herein, a “mid gate workfunction” is a work function typically between the conduction band andthe valence band of a semiconductor, such as silicon. In one embodiment,a mid gap gate work function may range from 4.5 eV to 4.6 eV. Themethods and structures of the present disclosure are now discussed ingreater detail with reference to FIGS. 1A-7B.

FIG. 1A depicts one embodiment of an electrical device including FinField Effect Transistors (FinFETs) that includes a semiconductorsubstrate 1 having a p-type region 10, a mid gap region 15, and ann-type region 20. Each of the FinFETs includes a channel region that ispresent in a fin structure 5 a, 5 b, 5 c. Each fin structure 5 a, 5 b, 5c may be composed of a semiconductor material. In some embodiments, thefin structures 5 a, 5 b, 5 c are composed of a type IV semiconductor,such as silicon (Si), e.g., single crystal silicon. It is noted that thepresent disclosure is not limited to only silicon, because othermaterials may be used for the composition of the fin structures, such asgermanium, silicon germanium, and compound semiconductors, such as typeIII-V semiconductor materials. Each of the fin structures 5 a, 5 b, 5 care present on a dielectric layer 2, which may be the buried oxide layerof a semiconductor on insulator (all) substrate.

A p-type FinFET (p-FinFET) device 100 a is present in the p-type region10 having a p-type work function gate structure 50 a present on thechannel region of the fin structure 5 a in the p-type region 10 of thesubstrate 1. The p-type work function gate structure 50 a may becomposed of a high-k gate dielectric 51 that is present on the channelregion of the fin structure 5 a; first metal containing buffer layer 52present on the first high-k gate dielectric 51; a first titanium nitridelayer 53 having a first thickness present on the first metal containingbuffer layer, and a first gate conductor contact 54 present on the firsttitanium nitride layer 51. The first thickness of the first titaniumnitride layer is selected to provide a p-type work function. In someembodiments, the p-type work function gate structure 50 a is present onthe top surface as well as the sidewall surfaces of the fin structure 5a that is present in the p-type region 10 of the substrate 1.

The term “high-k” denotes that the dielectric constant of the high-kdielectric material, such as the first high-k dielectric 51, is greaterthan the dielectric constant of silicon oxide at room temperature, e.g.,20° C. to 25° C. In some embodiments, the high-k dielectric material mayhave a dielectric constant of 4.0 or higher. In another example, thehigh-k dielectric material may have a dielectric constant greater than7.0. In one embodiment, the high-k dielectric material for the firsthigh-k dielectric 51 may be an oxide, such as hafnium oxide (HfO₂), orthe first high-k dielectric 51 may be a nitride, such as siliconnitride, e.g., Si₃N₄. In other embodiments, the first high-k dielectric51 may be selected from BN, ZrO₂, Al₂O₃, TiO₂, La₂O₃, SrTiO₃, LaAlO₃,Y₂O₃ and mixtures thereof. The first high-k dielectric 51 may also beselected from hafnium silicon oxide, hafnium silicon oxynitride,zirconium silicon oxide, zirconium silicon oxynitride, tantalum oxide,titanium oxide, barium strontium titanium oxide, barium titanium oxide,strontium titanium oxide, yttrium oxide, aluminum oxide, lead scandiumtantalum oxide, lead zinc niobate, nitrided hafnium silicate (HfSiON),lanthanum oxide (La₃O₂), zirconium silicate (ZrSiO_(x)) and combinationsthereof, so long as the material combinations selected provide for etchselectivity in accordance with the following described process flow. Thefirst high-k gate dielectric 51 may have a thickness ranging from 1 nmto 10 nm. In one example, the first high-k gate dielectric 51 has athickness ranging from 2 nm to 5 nm. In some embodiments, the firsthigh-k gate dielectric 51 is present on the upper surface of the portionof the fin structure 5 a that provides the channel region of the device,the sidewall portion of the fins structure 5 a, and the sidewalls of thegate spacer, which provides a u-shaped geometry, as depicted in FIG. 1A.

The first metal containing buffer layer 52 may be a metal nitride. Forexample, the first metal containing buffer layer 52 may be composed oftantalum nitride (TaN). It is noted that the present disclosure is notlimited to only tantalum nitride for the composition of the first metalcontaining buffer layer 52. For example, another metal nitride that issuitable for the first metal containing buffer layer may be tungstennitride (WN). It is noted that other compositions may also be possible,with one requirement being that the composition of the first metalcontaining buffer layer 52 may provide that the later deposited titaniumnitride layers can be removed selectively to the first metal containingbuffer layer 52. The thickness of the first metal containing bufferlayer 52 may range from 0.3 nm to 5 nm. In one example, the thickness ofthe first metal containing buffer layer 52 may range from 2 nm to 5 nm.The first metal containing buffer layer may be in direct contact withthe first high-k dielectric layer 51.

In some embodiments, the p-type FinFET (p-FinFET) device 100 a mayinclude a first titanium nitride layer 53 having a first thickness toprovide a p-type work function. The first titanium nitride layer 53 hasa thickness greater than the second titanium nitride layer 55 that ispresent in the gate structure 50 b for the mid gate FinFET 100 b, and isgreater than the titanium nitride layer (not shown) that is present inthe n-type FinFET 100 c (when a titanium nitride layer is present in then-type FinFET). For example, the thickness of the first titanium nitridelayer 53 may range from 3 nm to 12 nm. In another example, the thicknessof the first titanium nitride layer 53 may range from 5 nm to 10 nm.

A first gate conductor contact 54 may be present on, e.g., in directcontact with, the first titanium nitride layer. The first gate conductorcontact 54 may be composed of a gate electrode material such as aluminum(Al), tungsten (W), copper (Cu), as well as other work functionadjusting metals, and alloys thereof.

The p-type FinFET (p-FinFET) device 100 a may also include gatesidewalls spacers 56 that are present on the sidewalls of the p-typework function gate structure 50 a. The gate sidewall spacers 56 may becomposed of a dielectric material. P-type conductivity source and drainregions 57 are present on source and drain portions of the fin structure5 a. The p-type source and drain regions 57 may be composed of in situdoped epitaxial semiconductor material that is formed on the finstructures 5 a. In some embodiments, the epitaxial semiconductormaterial may be composed of silicon or silicon germanium.

Still referring to FIG. 1A, the mid gap semiconductor FinFET 100 b ispresent in the mid gap region 15 of the semiconductor substrate 1 havinga mid gap gate structure 50 b comprised of a second high-k gatedielectric 58, a second metal containing buffer layer 59 present on thesecond high-k gate dielectric 58, a second titanium nitride layer 55having a second thickness that is less than the thickness of the firsttitanium nitride layer 53 present on the second metal containing bufferlayer 52, and a second gate conductor contact 60 present on the secondtitanium nitride layer 55.

The second high-k gate dielectric 58 of the mid gap gate structure 50 bis similar to the first high-k gate dielectric layer 51 of the p-typegate structure 50 a. Therefore, the description of the first high-k gatedielectric layer 51 of the p-type gate structure 50 a may be suitablefor describing the second high-k gate dielectric 58 of the mid gap gatestructure 50 b. For example, the second high-k gate dielectric 58 of themid gap gate structure 50 b may be composed of hafnium oxide and have athickness ranging from 1 nm to 10 nm. The second high-k gate dielectric58 may be in direct contact with the channel region portion of the finstructure 5 b along the upper surface of the fin structure 5 b and thesidewall surfaces of the fin structure 5 b. The second high-k gatedielectric 58 may have the same or a different composition than thefirst high-k gate dielectric 51.

The second metal containing buffer layer 59 of the mid gap gatestructure 50 b is similar to the first metal containing buffer layer 52of the p-type gate structure 50 a. Therefore, the description of thefirst metal containing buffer layer 52 of the p-type gate structure 50 amay be suitable for describing the second metal containing buffer layer59 of the mid gap gate structure 50 b. For example, the second metalcontaining buffer layer 59 may be composed of tantalum nitride (TaN),and may have a thickness ranging from 0.3 nm to 5 nm. The second metalcontaining buffer layer 59 may have the same or a different compositionthan the first metal containing buffer layer 52.

In some embodiments, the mid gap FinFET (mid gap FinFET) device 100 bmay include a second titanium nitride layer 55 having a second thicknessto provide a mid gap work function. In one example, the thickness of thesecond titanium nitride layer 55 is selected so that the work functionis approximately 4.5 eV to 4.6 eV. The second titanium nitride layer 55has a thickness that is less than the first titanium nitride layer 53that is present in the p-type work function gate structure 50 a for thep-type FinFET 100 a, and is greater than the titanium nitride layer (notshown) that is present in the n-type FinFET 100 c (when a titaniumnitride layer is present in the n-type FinFET). For example, thethickness of the second titanium nitride layer 55 may range from 1 nm to3 nm. In one example, the thickness of the second titanium nitride layer55 may be less than 2 nm. A second gate conductor contact 60 may bepresent on, e.g., in direct contact with, the second titanium nitridelayer 55. The second gate conductor contact 60 may be composed of a gateelectrode material such as aluminum (Al), tungsten (W), copper (Cu), aswell as other work function adjusting metals, and alloys thereof. Thesecond gate conductor contact 60 may have the same or a differentcomposition than the first gate conductor contact 54.

Similar to the p-type FinFET 100 a, the mid gap FinFET 100 b alsoincludes a gate sidewall spacer 26 and source and drain regions 27. Thesource and drain regions 27 for the mid gap FinFET 100 b may have ann-type or p-type conductivity. In some embodiments, the source and drainregions 27 may be present on the source and drain region portions of thefin structure 5 b in the mid gap region 15 of the substrate 1. Thesource and drain regions 27 for the mid gap FinFET 100 b may be composedof in situ doped epitaxial semiconductor material that is formed on thefin structures 5 b. In some embodiments, the epitaxial semiconductormaterial may be composed of silicon, silicon doped with carbon (Si:C) orsilicon germanium.

Still referring to FIG. 1A, an n-type semiconductor device 100 c ispresent in the n-type region 20 having an n-type work function gatestructure 50 c comprised of a third high-k gate dielectric 61 present ona channel region of the n-type semiconductor device, a third metalcontaining buffer layer 62 on the third high-k gate dielectric and athird gate conductor fill 63 present atop the third metal containingbuffer layer 62.

The third high-k gate dielectric 61 of the n-type gate structure 50 c issimilar to the first high-k gate dielectric layer 51 of the p-type gatestructure 50 a, and the second high-k gate dielectric layer 58.Therefore, the description of the first high-k gate dielectric layer 51of the p-type gate structure 50 a may be suitable for describing thethird high-k gate dielectric 61 of the n-type gate structure 50 c. Forexample, the third high-k gate dielectric 61 of the n-type gatestructure 50 c may be composed of hafnium oxide and have a thicknessranging from 1 nm to 10 nm. The third high-k gate dielectric 61 may bein direct contact with the channel region portion of the fin structure 5c along the upper surface of the fin structure 5 c and the sidewallsurfaces of the fin structure 5 c. The third high-k gate dielectric 61may have the same or a different composition than the first high-k gatedielectric 51, and may have the same or different composition than thesecond high-k gate dielectric 58.

The third metal containing buffer layer 62 of the mid gap gate structure50 c is similar to the first metal containing buffer layer 52 of thep-type gate structure 50 a. Therefore, the description of the firstmetal containing buffer layer 52 of the p-type gate structure 50 a maybe suitable for describing the third metal containing buffer layer 62 ofthe n-type gate structure 50 c. For example, the third metal containingbuffer layer 62 may be composed of tantalum nitride (TaN), and may havea thickness ranging from 0.3 nm to 5 nm. The third metal containingbuffer layer 62 may have the same or a different composition than thefirst metal containing buffer layer 52, and may have the same or adifferent composition than the second metal containing buffer layer 59.

In some embodiments, the n-type work function gate structure 50 c of then-type FinFET device 100 c may not include, i.e., is entirely free, of atitanium nitride layer. As indicated above, both the p-type workfunction gate structure 50 a of the p-type FinFET 100 a and the mid gapwork function gate structure 50 b of the mid gap FinFET 100 b includetitanium nitride layers 53, 55 having thicknesses adjusted to provide awork function that is optimal for the p-type FinFET 100 a and the midgap FinFET 100 b. In some embodiments of the n-type work function gatestructure 50 c the third gate conductor contact 63 is in direct contactwith the third metal containing buffer layer 62. In some embodiments,the n-type work function gate structure 50 c provides an n-type workfunction without a titanium nitride layer. In other embodiments, then-type work function gate structure 50 c includes a third titaniumnitride layer (not shown) that is present between the third metalcontaining buffer layer 62 and the third gate conductor contact 63. Inthese embodiments, the thickness, i.e., third thickness, of the thirdtitanium nitride layer is less than the thickness, i.e., secondthickness, of the second titanium nitride layer 55 that is present inthe n-type work function gate structure 50 b. For example, the thicknessof the third titanium nitride layer 55 may range from 0 nm to 1 nm.

A third gate conductor contact 64 may be present on, e.g., in directcontact with, the second titanium nitride layer 55. The third gateconductor contact 64 may be composed of a gate electrode material suchas aluminum (Al), tungsten (W), copper (Cu), as well as other workfunction adjusting metals, and alloys thereof. The third second gateconductor contact 64 may have the same or a different composition thanthe first gate conductor contact 54

It is noted that the FinFETs depicted in FIG. 1A are only one embodimentof the present disclosure. The p-type work function gate structure 50 a,the mid gap work function gate structure 50 b and the n-type workfunction gate structure 50 c that are depicted in FIG. 1A are equallysuitable for planar semiconductor devices, such as field effecttransistors (FETs) formed on bulk semiconductor substrates, FETs formedon semiconductor on insulator (SOI) substrates, and FETs formed onextremely thin semiconductor on insulator (ETSOI) substrates, asdepicted in FIG. 1B.

Semiconductor on insulator (SOI) substrate included a base supportingsemiconductor layer; a dielectric layer present on the base supportingsemiconductor layer, e.g., a buried oxide layer; and an uppersemiconductor layer that is present on the dielectric layer, which maybe referred to as an SOI layer, and may be composed of silicon (Si).Extremely thin semiconductor on insulator (ETSOI) substrates are a formof SOI substrates. In ETSOI substrates, the thickness of the SOI layeris less than 10 nm, and typically less than 5 nm. Referring to FIG. 1B,it is noted that the portion of the semiconductor substrate 1 in whichthe semiconductor devices are formed may be composed of silicon,germanium, silicon germanium, and compound semiconductors, such as typeIII-V semiconductor materials.

FIG. 1B depicts one embodiment of an electrical device including p-typeplanar semiconductor devices 100 d, mid gate planar semiconductordevices 100 e and mid gate planar semiconductor devices 100 f. Each ofthe p-type planar semiconductor device 100 d, the mid gap planarsemiconductor device 100 e and the n-type planar semiconductor device100 f are hereafter referred to as being field effect transistors(FETs).

The gate structure for the p-type FET 100 d is a p-type work functiongate structure 50 a that is present on the channel region of the uppersurface of the semiconductor substrate 1 in the p-type region of thesubstrate 1. The material layers and composition of the material layersin the p-type work function gate structure 50 a of the p-type FET 100 dis similar to the material layers and composition of the p-type workfunction gate structure 50 a of the p-type FinFET 100 a. For example,the p-type work function gate structure 50 a of p-type FET 100 d may becomposed of a high-k gate dielectric 51 that is present on the channelregion of the semiconductor substrate 1 in the p-type region 10; a firstmetal containing buffer layer 52 present on the first high-k gatedielectric 51; a first titanium nitride layer 53 having a firstthickness present on the first metal containing buffer layer, and afirst gate conductor contact 54 present on the first titanium nitridelayer 51. The first thickness of the first titanium nitride layer isselected to provide a p-type work function. Each of the aforementionedlayers have been described above in the description of the layers havingthe same reference numbers for the p-type work function gate structure50 a of the p-type FinFET 100 a.

In one example, the p-type work function gate structure 50 a of thep-type FET 100 d includes a first high-k gate dielectric 51 of hafniumoxide having a thickness ranging from 1 nm to 10 nm; a first metalcontaining buffer layer 52 composed of tantalum nitride (TaN) and havinga thickness ranging from 0.3 nm to 5 nm; a first titanium nitride layer53 having a thickness selected to provide a p-type work function; and agate conductor contact 64 composed of a metal such as copper, aluminumor tungsten. The thickness of the first titanium nitride layer 53 mayrange from 3 nm to 12 nm in order to provide a p-type work function.

The p-type FET 100 d may also include gate sidewalls spacers 56 that arepresent on the sidewalls of the p-type work function gate structure 50a. P-type conductivity source and drain regions 64 are present in thesemiconductor substrate 1 on opposing sides of the p-type work functiongate structure 50 a. In some embodiments, the source and drain regions64 may be raised by forming epitaxial semiconductor material on theupper surface of the semiconductor substrate 1.

The gate structure for the mid gap FET 100 e is a mid gap work functiongate structure 50 b that is present on the channel region of the uppersurface of the semiconductor substrate 1 in the p-type region of thesubstrate 1. The material layers and composition of the material layersin the mid gap work function gate structure 50 b of the mid gap FET 100e is similar to the material layers and composition of the mid gap workfunction gate structure 50 b of the mid gap FinFET 100 b. For example,the mid gap gate structure 50 e of mid gap FET 100 e may be composed ofa second high-k gate dielectric 58 that is present on the channel regionof the semiconductor substrate 1 in the mid gap region 15; a secondmetal containing buffer layer 59 present on the second high-k gatedielectric 58; a second titanium nitride layer 55 having a secondthickness present on the second metal containing buffer layer, and asecond gate conductor contact 50 present on the second titanium nitridelayer 55. The second thickness of the first titanium nitride layer isselected to provide a mid gap work function. Each of the aforementionedlayers have been described above in the description of the layers havingthe same reference numbers for the mid gap work function gate structure50 b of the mid gap FinFET 100 b.

In one example, the mid gap work function gate structure 50 b of the midgap FET 100 e includes a first high-k gate dielectric 58 of hafniumoxide having a thickness ranging from 1 nm to 10 nm; a second metalcontaining buffer layer 59 composed of tantalum nitride (TaN) and havinga thickness ranging from 0.3 nm to 5 nm; a second titanium nitride layer55 having a thickness selected to provide a mid gap work function; and agate conductor contact 60 composed of a metal such as copper, aluminumor tungsten. The thickness of the second titanium nitride layer 55 mayrange from 1 nm to 3 nm in order to provide a mid gap work function. Thethickness of the second titanium nitride layer 55 is less than thethickness of the titanium nitride layer, i.e., first titanium nitridelayer 53, in the p-type work function gate 50 a, and is greater than thethickness of the third titanium layer (not shown) in the n-type workfunction gate structure 50 c.

The mid gap FET 100 e may also include gate sidewalls spacers 56 thatare present on the sidewalls of the mid gap gate structure 50 b. P-typeconductivity source and drain regions 64 b or n-type source and drainregions are present in the semiconductor substrate 1 on opposing sidesof the mid gap work function gate structure 50 b. In some embodiments,the source and drain regions 64 b may be raised by forming epitaxialsemiconductor material on the upper surface of the semiconductorsubstrate 1.

The gate structure for the n-type FET 100 f is an n-type work functiongate structure 50 c that is present on the channel region of the uppersurface of the semiconductor substrate 1 in the n-type region 20 of thesubstrate 1. The material layers and composition of the material layersin the n-type work function gate structure 50 c of the n-type FET 100 fare similar to the material layers and composition of the n-type workfunction gate structure 50 c of the n-type FinFET 100 c. For example,the n-type work function gate structure 50 c of p-type FET 100 e may becomposed of a third high-k gate dielectric 61 that is present on thechannel region of the semiconductor substrate 1 in the n-type region 20;a third metal containing buffer layer 62 present on the third high-kgate dielectric 51; and a third gate conductor contact 63 present on thethird metal containing buffer layer 62. In some embodiments of then-type work function gate structure 50 c the third gate conductorcontact 63 is in direct contact with the third metal containing bufferlayer 62.

In one example, the n-type work function gate structure 50 c of then-type FET 100 f includes a third high-k gate dielectric 61 of hafniumoxide having a thickness ranging from 1 nm to 10 nm; a third metalcontaining buffer layer 62 composed of tantalum nitride (TaN) and havinga thickness ranging from 0.3 nm to 5 nm; and a gate conductor contact 63composed of a metal such as copper, aluminum or tungsten.

In some embodiments, the n-type work function gate structure 50 c of then-type FET 100 f provides an n-type work function without a titaniumnitride layer. In other embodiments, the n-type work function gatestructure 50 c includes a third titanium nitride layer (not shown) thatis present between the third metal containing buffer layer 62 and thethird gate conductor contact 63. In these embodiments, the thickness,i.e., third thickness, of the third titanium nitride layer is less thanthe thickness, i.e., second thickness, of the second titanium nitridelayer 55 that is present in the n-type work function gate structure 50b. For example, the thickness of the third titanium nitride layer 55 mayrange from 0 nm to 1 nm.

The n-type FET 100 f may also include gate sidewalls spacers 56 that arepresent on the sidewalls of the n-type work function gate structure 50c. N-type conductivity source and drain regions 64 c are present in thesemiconductor substrate 1 on opposing sides of the n-type work functiongate structure 50 c. In some embodiments, the source and drain regions64 c may be raised by forming epitaxial semiconductor material on theupper surface of the semiconductor substrate 1.

Isolation between the p-type FET 100 d, the mid gap FET 100 e and then-type FET 100 f may be provided by an isolation region 65 positionedbetween the aforementioned devices. The isolation region 65 may be atrench isolation region filled with a dielectric material, such assilicon oxide.

It is noted that although FIG. 1B depicts a bulk semiconductorsubstrate, the p-type FET 100 d, the mid gap FET 100 e, and the n-typeFET 100 f may also be formed on an SOI substrate or an ETSOI substrate.Additionally, it is not necessary that each of the p-type FinFET 100 a,the mid gap FinFET 100 b, the n-type FinFET 100 c, the p-type FET 100 d,the mid gap FET 100 e, and the n-type FET 100 f are present on the samesubstrate 1, as the any of the aforementioned devices may be present onthe same substrate in any combination.

Further details regarding the structures depicted in FIGS. 1A and 1B maybe provided in the following description of a method of formingsemiconductor devices in which the work function of a gate structure maybe adjusted by adjusting the thickness of titanium nitride layers withinthe gate structures. FIGS. 2A-6A illustrate one embodiment of formingFinFET type devices, such as the FinFETs depicted in FIG. 1A. FIGS.2B-6B illustrate one embodiment of forming planar FET devices, such asthe FETs depicted in FIG. 1B.

FIG. 2A depicts one embodiment of forming a sacrificial gate structure70 on a plurality of fin structures 5 a, 5 b, 5 c, in which one of thefin structures 5 a is for p-type FinFET device 100 a, one of the finstructures 5 b is for a mid gap finFET device 100 b and one of the finstructures 5 c is for an n-type device 100 c. The fin structures 5 a, 5b, 5 c may be formed from a semiconductor substrate 1 using patterningand etching, e.g., spacer image transfer (SIT) processing. The finstructures 5 a, 5 b, 5 c may have a height ranging from 5 nm to 200 nm.In another embodiment, the fin structures 5 a, 5 b, 5 c may have aheight ranging from 10 nm to 100 nm. The fin structures 5 a, 5 b, 5 cmay each have a width of less than 20 nm. In another embodiment, the finstructures 5 a, 5 b, 5 c have a width ranging from 5 nm to 20 nm.

The sacrificial gate structure 70 is an element of a replacement gateprocess. The term “sacrificial” as used to describe the replacementstructure denotes that the structure is present during the processsequence, but is not present in the final device structure, in which thesacrificial structure provides an opening that dictates the size andgeometry of a later formed functional gate structure. In someembodiments, the sacrificial gate structures 70 that are depicted inFIG. 2A are formed of a semiconductor material, such as polysilicon.But, in other embodiments, the sacrificial gate structures 70 may becomposed of a dielectric material. The sacrificial gate structures 70may be formed using deposition, photolithography and etching processes.The sacrificial gate structures 70 are formed to have a geometry thatmatches the geometry of the later formed functional gate structures. Inthe embodiment that is depicted in FIG. 2A, a sacrificial gate structure70 is formed for each fin structure 5 a, 5 b, 5 c for each of the p-typeFinFET 100 a, the mid gap FinFET 100 b, and the n-type FinFET 100 c.

FIG. 2B depicts forming the sacrificial gate structure 70 on the channelregion of the p-type region 10, mid gap region 15 and the n-type region20 of the semiconductor substrate 1 for the planar devices. e.g., p-typeFET 100 d, mid gap FET 100 e and n-type FET 100 f.

Referring to FIGS. 2A and 2B, a gate sidewall spacer 56 may then beformed on each of the sacrificial gate structures 70. The gate sidewallspacer 56 may be composed of oxide, i.e., SiO₂, but may also comprisenitride or oxynitride materials. Each gate sidewall spacer 56 can beformed by deposition and etch processes.

FIG. 2A also depicted forming the source and drain regions 57 a, 57 b,57 c on opposing sides of the sacrificial gate structures 70 that arepresent in the p-type region 10, mid gap region 15 and the n-type region20. The source and drain regions 57 a, 57 b, 57 c are formed on thesource and drain region portions of the fin structures 5 a, 5 b, 5 c.The conductivity type of the source and the drain regions typicallydictates the conductivity type of the semiconductor device. The term“conductivity type” refers to whether the device is n-type or p-type.The conductivity type of the source and drain regions typically dictatethe conductivity type of the device. For example, if the source anddrain regions are doped to an n-type conductivity, the semiconductordevice may be referred to as an n-type conductivity device, such as ann-FinFET, and if the source and drain regions are doped to a p-typeconductivity, the semiconductor device may be referred to as a p-typeconductivity device, such as a p-FinFET. As used herein, “n-type” refersto the addition of impurities that contributes free electrons to anintrinsic semiconductor. As used herein, “p-type” refers to the additionof impurities to an intrinsic semiconductor that creates deficiencies ofvalence electrons.

The source and drain regions 57 a, 57 b, 57 c may be formed by ionimplanting n-type or p-type dopant into the source and drain regionportions of the fin structures 5 a, 5 b, 5 c. The source and drainregions 57 a, 57 b, 57 c may also be formed by forming in-situ dopedn-type or p-type conductivity epitaxial semiconductor material on thesource and drain region portions of the fin structures 30 a, 30 b. Insome embodiments, a combination of ion implantation and in-situ dopedn-type or p-type conductivity epitaxial semiconductor material may beemployed to form the source and drain regions 57 a, 57 b, 57 c. Blockmasks may be utilized to isolate specific fin structures 30 a, 30 b foreach conductivity type doping required. As explained above, the sourceand drain regions 57 a in the p-type region 10 are doped to a p-typeconductivity; the source and drain regions 57 b in the mid gap region 15are doped to an n-type or p-type conductivity; and the source and drainregions 57 c in the m-type region 20 are doped to an n-typeconductivity. The concentration of dopant within the source and drainregions 57 a, 57 b, 57 c is typically present in a concentration rangingfrom about 10¹¹ to about 10¹⁵ atoms/cm², with a concentration of dopantwithin the doped region from about 10¹¹ to about 10¹³ atoms/cm² beingmore typical.

FIG. 2B depicts implanting dopants into the semiconductor substrate 1 toform the source and drain regions 65 a, 65 b, 65 c of planarsemiconductor devices, e.g., the planar p-type FET 100 e, the planar midgap FET 100 f, and the planar n-type FET 100 g. The source regions anddrain regions 65 a, 65 b, 65 c for the planar semiconductor devices areformed ion implantation. Block masks may be utilized to isolate specificregions, e.g., p-type region 10, mid gap region 15 and n-type region 20,for each conductivity type doping required. Although FIG. 2B onlydepicts forming source and drain regions 65 a, 65 b, 65 c within thesurface of the substrate 10, the present disclosure is not limited toonly this example. For example, raised source and drain regions (notshown) may be present on the upper surfaces of the semiconductorsubstrate on opposing sides of the sacrificial gate structure 70. Theraised source and drain regions may be formed of epitaxially depositedsemiconductor material and may have the same dopant conductivity as thesource and drain regions 65 a, 65 b, 65 c that the epitaxial material isformed on.

The method may continue with activating the source and drain regions 57a, 57 b, 57 c, 65 a, 65 b, 65 c. Activation of the source and drainregions 57 a, 57 b, 57 c, 65 a, 65 b, 65 c may be done with thesacrificial gate structure 70 present on the substrate 1. This providesthat the later formed functional gate structure is not subjected to thehigh temperature anneal process.

FIGS. 2A and 2B also depict forming an interlevel dielectric layer 71having an upper surface that is coplanar with the upper surface of thesacrificial gate structure 70. The interlevel dielectric layer 71 may bedeposited using chemical solution deposition, spin on deposition,chemical vapor deposition or a combination thereof. The interleveldielectric layer 71 may be selected from the group consisting of siliconcontaining materials such as SiO₂, Si₃N₄, SiO_(x)N_(y), SiC, SiCO,SiCOH, and SiCH compounds, the above-mentioned silicon containingmaterials with some or all of the Si replaced by Ge, carbon dopedoxides, inorganic oxides, inorganic polymers, hybrid polymers, organicpolymers such as polyamides or SiLK™, other carbon containing materials,organo-inorganic materials such as spin-on glasses andsilsesquioxane-based materials, and diamond-like carbon (DLC), alsoknown as amorphous hydrogenated carbon, α-C:H). Additional choices forthe interlevel dielectric layer 71 include any of the aforementionedmaterials in porous form, or in a form that changes during processing toor from being porous and/or permeable to being non-porous and/ornon-permeable. Following deposition, the interlevel dielectric layer 71may be planarized to provide an upper surface that is coplanar with anexposed upper surface of the replacement gate structures 70. In oneexample, the planarization process is chemical mechanical planarization(CMP).

FIGS. 3A and 3B depicting removing the sacrificial gate structure fromthe structures depicted in FIGS. 2A and 2B. Once, the sacrificial gatestructures 70 are exposed by the aforementioned chemical mechanicalplanarization (CMP) process, they may be removed using a selective etchprocess. As used herein, the term “selective” in reference to a materialremoval process denotes that the rate of material removal for a firstmaterial is greater than the rate of removal for at least anothermaterial of the structure to which the material removal process is beingapplied. In some embodiments, the sacrificial gate structures 70 areremoved by an etch that is selective to the interlevel dielectric, thegates sidewall spacers 56, and the semiconductor structure that thechannel region is present therein, such as the fin structures 5 a, 5 b,5 c, as depicted in FIG. 3A, or the semiconductor substrate 1, asdepicted in FIG. 3B. The etch process may be an anisotropic etch, suchas reactive ion etch, or an isotropic etch, such as a wet chemical etch.Removing the sacrificial gate structures 70 provides a gate opening tothe channel regions of the devices.

FIG. 3A depicts forming a first high-k dielectric 51, second high-kdielectric 58, and a third high-k dielectric 61 on each of the finstructures 5 a, 5 b, 5 c for the p-type FinFET 100 a, the mid gap FinFET100 b and the n-type FinFET 100 c. In some embodiments, the first high-kdielectric 51, the second high-k dielectric 58, and the third high-kdielectric 61 is formed using a deposition process such as, for example,chemical vapor deposition (CVD), plasma-assisted CVD, metal-organicchemical vapor deposition (MOCVD), atomic layer deposition (ALD),evaporation, reactive sputtering, chemical solution deposition and otherlike deposition processes. The first high-k dielectric 51, the secondhigh-k dielectric 58, and the third high-k dielectric 61 may also beformed utilizing any combination of the above processes. The high-kdielectrics are typically deposited as a conformal layer using aconformal deposition process. The term “conformal” denotes a layerhaving a thickness that does not deviate from greater than or less than30% of an average value for the thickness of the layer. The materiallayer for the first high-k dielectric 51, the second high-k dielectric58, and the third high-k dielectric 61 may be a blanket deposited layerthat is formed on the upper surface of the interlevel dielectric layer71; the sidewall surface of the gate sidewall spacer 56 that providesthe sidewall of the gate opening; and the base of the gate openingprovided by the channel region of the devices, i.e., p-type FinFET 100a, mid gap FinFET 100 b and the n-type FinFET 100 c. The portion of thematerial layer that is present on the upper surface of interleveldielectric 71 that provides the first high-k dielectric 51, the secondhigh-k dielectric 58, and the third high-k dielectric 61 may be removedby a planarization process, such as chemical mechanical planarization(CMP).

The high-k gate dielectric layer 51′ may be composed of a singlecomposition high-k dielectric layer that provides the same compositionfor the each of the p-type FinFET 100 a, the mid gap FinFET 100 b andthe n-type FinFET 100 c. In some embodiments, the material layers forthe high-k dielectric layer for each of the p-type FinFET 100 a, the midgap FinFET 100 b and the n-type FinFET 100 c may be formed independentlyfrom one another. This can be accomplished using block masks, asdescribed in the above embodiments. By employing block masks, at leastone of the material layers for at least one of the p-type FinFET 100 a,the mid gap FinFET 100 b and the n-type FinFET 100 c may have acomposition that is different than the material layers in the remainingp-type FinFET 100 a, the mid gap FinFET 100 b and the n-type FinFET 100c.

FIG. 3B depicts forming a high-k gate dielectric 51′ on each of thechannel regions for the planar p-type FET 100 e, the planar mid gap FET100 f and the planar n-type FET 100 g. The description of the high-kgate dielectric 51′ described with reference to FIG. 3A is suitable forthe description of the high-k gate dielectric 51′ that is depicted inFIG. 3B.

FIG. 4A depicts forming a gate stack of a metal containing buffer layer52′ on the high-k gate dielectric 51′ depicted in FIG. 3A and a firsttitanium nitride layer 53′ having a first thickness on the metal bufferlayer 52′. The thickness of the first titanium nitride layer 53′ istypically selected to provide a p-type work function for the p-type workfunction gate structure 50 a of the p-type FinFET 100 a. As will bediscussed in greater detail below, the thickness of the first titaniumnitride layer 53′ may be reduced or removed from the regions of thesubstrate, in which the mid gap FinFET 100 b and the n-type FinFET 100 care present. For example, in the mid gap region 15 the first titaniumnitride layer 53′ may be patterned and etched to have a second thicknessthat is less than the thickness of the portion of the first titaniumnitride layer 53′ that is present in the p-type region 10 of thesubstrate; and to have a greater thickness than the portion of the firsttitanium nitride layer 53′ that is present in the n-type region 20 ofthe substrate, i.e., if the first titanium nitride layer 53′ that isremoved in its entirety from the n-type region 20.

The metal containing buffer layer 52′ may be a metal nitride. Forexample, the metal containing buffer layer 52′ may be composed oftantalum nitride (TaN). The thickness of the metal containing bufferlayer 52′ may range from 0.3 nm to 5 nm. In one example, the thicknessof the metal containing buffer layer 52′ may range from 3 nm to 5 nm.The metal containing buffer layer 52′ may be conformally depositeddirectly on the high-k dielectric layer 51′. The metal containing bufferlayer 52′ may be a blanket deposited layer that is formed over the uppersurface of the interlevel dielectric layer 71; the sidewall surface ofthe gate sidewall spacer 56 that provides the sidewall of the gateopening; and the base of the gate opening provided by the channel regionof the devices, i.e., p-type FinFET 100 a, mid gap FinFET 100 b and then-type FinFET 100 c. The metal containing buffer layer 52′ may bedeposited using atomic layer deposition (ALD). The metal containingbuffer layer 52′ may also be formed using a physical vapor deposit (PVD)process, such as sputtering or plating. In other embodiments, the metalcontaining buffer layer 52′ may also be deposited using chemical vapordeposition, such as plasma enhanced chemical vapor deposition (PECVD).

The first titanium nitride layer 53′ may be conformally depositeddirectly on the metal containing buffer layer 52′. The first titaniumnitride layer 53′ may be a blanket deposited layer that is formeddirectly on the metal containing buffer layer 52′, and over the uppersurface of the interlevel dielectric layer 71; the sidewall surface ofthe gate sidewall spacer 56 that provides the sidewall of the gateopening; and the base of the gate opening provided by the channel regionof the devices, i.e., p-type FinFET 100 a, mid gap FinFET 100 b and then-type FinFET 100 c. The first titanium nitride layer 53′ may bedeposited using atomic layer deposition (ALD). The first titaniumnitride layer 53′ may also be formed using a physical vapor deposit(PVD) process, such as sputtering or plating. In other embodiments, thefirst titanium nitride layer 53′ may also be deposited using chemicalvapor deposition, such as plasma enhanced chemical vapor deposition(PECVD).

FIG. 4B depicts forming a gate stack of a metal containing buffer layer52′ on the high-k gate dielectric 51, 58, 61 of the planar p-type FET100 a, the planar mid gap FET 100 b, and the n-type FET 100 c that isdepicted in FIG. 3B. FIG. 4B also depicts forming a first titaniumnitride layer 53′ having a first thickness on the metal containingbuffer layer 52′. The metal containing buffer layer 52′ and the firsttitanium nitride layer 53′ have been described in FIG. 4A.

FIG. 5A depicts forming a block mask 72 over the portion of firsttitanium nitride 53′ that is present on the fin structure 5 a for thep-type FinFET 100 a in the p-type region 10 of the substrate 1. Theblock mask 72 does not cover the portions of the first titanium nitridelayer 53′ that are present in the mid gap region 15 and n-type region 20of the substrate 1, leaving these portions of the first titanium nitridelayer 53′ exposed. The block mask 72 may comprise soft and/or hardmaskmaterials and can be formed using deposition, photolithography andetching. In one embodiment, the block mask 72 comprises a photoresist. Aphotoresist block mask can be produced by applying a photoresist layer,exposing the photoresist layer to a pattern of radiation, and thendeveloping the pattern into the photoresist layer utilizing conventionalresist developer. Typically, the block masks have a thickness rangingfrom 100 nm to 300 nm.

FIG. 5B depicting forming a block mask 72 over the portion of firsttitanium nitride 53′ that is present over the channel region for thep-type planar device 100 e that is depicted in FIG. 4B. The block mask72 has been described above with reference to FIG. 5A.

FIG. 6A depicts removing the exposed portions of the first titaniumnitride layer 53′ from the mid gap region 15 of the substrate 1, and then-type region 20 of the substrate, while the portion of the firsttitanium nitride layer 53′ that is present in the p-type region 10 ofthe substrate 1 is protected by the block mask 72. The exposed portionsof the first titanium nitride layer 53′ are removed by an etch processthat is selective to the underlying metal containing buffer layer 52′.The etch process for removing the exposed portions of the first titaniumnitride layer 53′ may be an isotropic etch, such as a wet chemical etch,and/or an anisotropic etch, such as reactive ion etching. In oneexample, when the metal containing buffer layer 52′ is composed oftantalum nitride (TaN), the exposed portions of the first titaniumnitride layer 53′ may be removed by a peroxide based etch chemistry,such as peroxide 60:1 at 65° C. The portion of the first titaniumnitride layer 53′ remains in the p-type region 10 of the substratehaving a thickness that is suitable for the first titanium nitride layer53 of the functional gate structure for the p-type FinFET 100 a. In someembodiments, instead of removing the first titanium nitride layer 53′ inits entirety from the mid gap region 15 and the n-type region 20 of thesubstrate 1, the exposed portion of the first titanium nitride layer 53′may be etched to reduce its thickness to a second thickness thatprovides a mid gap work function for the mid gap FinFET 100 b that ispresent in the mid gap region 15 of the semiconductor substrate 1.Additionally, in some embodiments, the portion of the first titaniumnitride layer 53′ may not be entirely removed from the n-type region 20of the substrate 1, but recessed to a third thickness that produces ann-type work function for the n-type FinFET 100 c, in which the thirdthickness is less than the aforementioned second thickness that producesa mid gap work function for the mid gap FinFETs 100 b.

FIG. 6B depicts removing the first titanium nitride layer 53′ from themid gap region 15 and the n-type region 20 of the semiconductorsubstrate 1, in which the first titanium nitride layer 53′ having thefirst thickness remains in the n-type region 10 of the semiconductorsubstrate 1 to provide a work function adjusting titanium nitride layerfor the functional gate structure of a planar p-type FET 100 d. Theexposed portions of the first titanium nitride layer 53′ are removedusing a selective etch. In some embodiments, instead of removing thefirst titanium nitride layer 53′ in its entirety from the mid gap region15 and the n-type region 20 of the substrate 1, the exposed portion ofthe first titanium nitride layer 53′ may be etched to reduce itsthickness to a second thickness that provides a mid gap work functionfor the mid gap FET 100 e that is present in the mid gap region 15 ofthe semiconductor substrate 1. Additionally, in some embodiments, theportion of the first titanium nitride layer 53′ may not be entirelyremoved from the n-type region 20 of the substrate 1, but recessed to athird thickness that produces an n-type work function for the planarn-type FET 100 f, in which the third thickness is less than theaforementioned second thickness that produces a mid gap work functionfor the mid gap FET 100 e. Further details for the etch process forreducing the thickness of the exposed portions of the first titaniumnitride layer 53′ or for removing the exposed portions of the firstnitride layer 53′ in their entirety have been provided in the abovedescription of FIG. 6A.

It is noted that in the etch process steps described with reference toFIGS. 6A and 6B, the high-k dielectric layers 58, 61 in the mid gapregion 15 and the n-type region 20 are protected by the metal containingbuffer layer 52′. The high-k dielectric layers 58, 61 are never exposedduring patterning of the first titanium nitride layer 53′. The presentintegration process is compatible with both oxide hard mask schemes andresist patterning schemes.

FIG. 7A depicts forming a second titanium nitride layer 55′ having asecond thickness that is less than the thickness of the first titaniumnitride layer 53′ on the channel region of the fin structure 5 b for themid gap FinFET 100 b. FIG. 7B depicts forming a second titanium nitridelayer 55′ having a second thickness that is less than the thickness ofthe first titanium nitride layer 53′ in the mid gap region 15 of thesemiconductor substrate 1 on the channel region of the planar mid gapFET 100 e.

In some embodiments, before forming the second titanium nitride layer55′, a second block mask (not shown), e.g., photoresist mask or hardmask, is formed over the n-type region 20 of the semiconductor substrate1. In some embodiments, the block mask 72 that is present over thep-type region 10 of the semiconductor substrate 1 during etching of theexposed portions of the first titanium nitride layer 53′ may remain overthe n-type region 20 of the substrate 1 during formation of the secondtitanium nitride layer 55. If the block mask 72 that was present overthe n-type region 20 has been removed, a new hard mask may be formedover the p-type region 10 prior to forming the second titanium nitridelayer 55′. The combination of masks used are employed to cover p-typeregion 10 and n-type region 10 of the substrate 1 leaving the mid gapregion 15 of the substrate 1 exposed. The second titanium nitride layer55′ may then be deposited on the exposed mid gap region 20 of thesubstrate. For example, the second titanium nitride layer 55′ may be ablanket deposited conformal layer having at least a portion in directcontact with the metal containing buffer layer 52′ in the gate openingwithin the mid gap region 15 of the substrate 1. The second titaniumnitride layer 55′ may also be formed using a physical vapor deposit(PVD) process, such as sputtering or plating. In other embodiments, thesecond titanium nitride layer 55′ may also be deposited using chemicalvapor deposition, such as plasma enhanced chemical vapor deposition(PECVD). The second titanium nitride layer 55′ may be deposited to asecond thickness that provides a mid gap work function for the mid gapFinFET 100 b that is present in the mid gap region 15 of thesemiconductor substrate 1, as depicted in FIG. 7A. The second titaniumnitride layer 55′ may be deposited to a second thickness that provides amid gap work function for the mid gap FET 100 e that is present in themid gap region 15 of the semiconductor substrate 1, as depicted in FIG.7B. The second thickness is less than the thickness of the firsttitanium nitride layer 53′ that is present in the p-type region 10 ofthe semiconductor substrate 1.

In some embodiments, the n-type region 20 of the semiconductor substrateis entirely free of titanium nitride layers that can be incorporatedinto a functional gate structure. In some other embodiments, a thirdtitanium nitride layer (not shown) may be deposited in the n-type regionof the semiconductor substrate 5 having a thickness that is less thanthe thickness of the second titanium nitride layer 55 that is present inthe mid gap region 15 of the semiconductor substrate 1. Block masks maybe utilized to cover the first and second titanium nitride layers 53′,55′ that are present in the p-type region 10 and the mid gap region 15of the substrate 1, while the third titanium nitride layer is formed inthe n-type region 20 of the substrate 1.

The block masks may then be removed using chemical stripping, selectiveetch or oxygen ashing.

In a following process step, the first gate conductor contact 54, thesecond gate conductor contact 60 and the third gate conductor contact 63are formed in the p-type region 10, the mid gap region 15 and the n-typeregion 20. The first gate conductor contact 54, the second gateconductor contact 60 and the third gate conductor contact 63 may bedeposited using a physical vapor deposition method. For example, thefirst gate conductor contact 54, the second gate conductor contact 60and the third gate conductor contact 63 may be deposited using plating,electroplating, electroless plating, sputtering and combinationsthereof. Examples of sputtering apparatus that may be suitable fordepositing the first gate conductor contact 54, the second gateconductor contact 60 and the third gate conductor contact 63 include DCdiode type systems, radio frequency (RF) sputtering, magnetronsputtering, and ionized metal plasma (IMP) sputtering. In addition tophysical vapor deposition (PVD) techniques, the first gate conductorcontact 54, the second gate conductor contact 60 and the third gateconductor contact 63 may also be formed using chemical vapor deposition(CVD).

In a following process step, the portions of the first gate conductorcontact 54, the second gate conductor contact 60, the third gateconductor contact 63, the first titanium nitride layer 53′, and thesecond titanium nitride layer 55′ that are present on the upper surfacesof the interlevel dielectric 71 may be removed using a planarizationprocess, such as chemical mechanical planarization (CMP), to provide thestructures depicted in FIGS. 1A and 1B. Following planarization, theremaining portion of the first titanium nitride layer 53′ provides thefirst titanium nitride layer 53 of the p-type FinFET 100 a, as depictedin FIG. 1A, and the p-type FET 100 e, as depicted in FIG. 1B. Followingplanarization, the remaining portion of the second titanium nitridelayer 55′ provides the second titanium nitride layer 55 of the mid gapFinFET 100 b, as depicted in FIG. 1A, and the mid gap FET 100 f, asdepicted in FIG. 1B.

In accordance with some embodiments, the methods and structures of thepresent disclosure provide that the high-k dielectric layers are notexposed to etch chemistries following their formation. The n-typesemiconductor devices may have superior leakage characteristics whencompared to prior methods of formation for similar structures.Additionally, the work function metal patterning scheme is compatiblewith both photoresist masks and hard masks, e.g., silicon oxide masks.

While the present invention has been particularly shown and describedwith respect to preferred embodiments thereof, it will be understood bythose skilled in the art that the foregoing and other changes in formsand details may be made without departing from the spirit and scope ofthe present invention. It is therefore intended that the presentinvention not be limited to the exact forms and details described andillustrated, but fall within the scope of the appended claims.

The invention claimed is:
 1. An electrical device comprising: asemiconductor substrate having an n-type region, a p-type region and amid gap region; a p-type semiconductor device present in the p-typeregion having a p-type work function gate structure comprised of a firsthigh-k gate dielectric, a first metal containing buffer layer present onthe first high-k gate dielectric, and a first titanium nitride layerhaving a first thickness present on the first metal containing bufferlayer; a mid gap semiconductor device present in the mid gap region ofthe semiconductor substrate having a mid gap gate structure comprised ofa second high-k gate dielectric, a second metal containing buffer layerpresent on the second high-k gate dielectric, and a second titaniumnitride layer having a second thickness that is less than the firstthickness present on the second metal containing buffer layer; whereinthe mid gap semiconductor device has a gate work function ranging from4.5 eV to 4.6 eV, and an n-type semiconductor device present in then-type region having an n-type work function gate structure comprised ofa third high-k gate dielectric present on a channel region of the n-typesemiconductor device, a third metal containing buffer layer on the thirdhigh-k gate dielectric and a n-type gate conductor contact present atopthe third metal containing buffer layer.
 2. The electrical device ofclaim 1, wherein the p-type semiconductor device further comprises ap-type gate conductor contact present on the first titanium nitridelayer, and the mid gap semiconductor device further comprises a mid gapgate conductor contact present on the second titanium nitride layer. 3.The electrical device of claim 1, wherein the n-type gate conductorcontact is in direct contact with the third metal containing bufferlayer.
 4. The electrical device of claim 1 further comprising a thirdtitanium nitride layer having a third thickness that is less than thesecond thickness, the third titanium nitride layer present on the thirdmetal containing buffer layer, wherein the n-type gate conductor contactis in direct contact with the third titanium nitride layer.
 5. Theelectrical device of claim 1, wherein the p-type semiconductor device isa p-type FinFET, the mid gap semiconductor device is a mid gap FinFET,and the n-type semiconductor device is an n-type FinFET.
 6. Theelectrical device of claim 1, wherein the p-type semiconductor device isa planar p-type FET, the mid gap semiconductor device is a planar midgap FET, and the n-type semiconductor device is planar n-type FET. 7.The electrical device of claim 6, wherein the semiconductor substrate isa bulk semiconductor substrate, a semiconductor on insulator (SOI)substrate, a extremely thin semiconductor on insulator (ETSOI)substrate, or a combination thereof.
 8. The electrical device of claim1, wherein at least one of the first metal containing buffer layer, thesecond metal containing buffer layer and the third metal containingbuffer layer comprises tantalum nitride (TaN).
 9. The electrical deviceof claim 1, wherein the first metal containing buffer layer, the secondmetal containing buffer layer and the third metal containing bufferlayer have a same composition.
 10. The electrical device of claim 1,wherein at least one of the first high-k gate dielectric, the secondhigh-k gate dielectric, and the third high-k gate dielectric compriseshafnium oxide, hafnium silicon oxide, hafnium silicon oxynitride,zirconium silicon oxide, zirconium silicon oxynitride, tantalum oxide,titanium oxide, barium strontium titanium oxide, barium titanium oxide,strontium titanium oxide, yttrium oxide, aluminum oxide, lead scandiumtantalum oxide, lead zinc niobate, nitrided hafnium silicate (HfSiON),lanthanum oxide (La₃O₂), zirconium silicate (ZrSiOx) or a combinationthereof.
 11. An electrical device comprising: a semiconductor substratehaving an n-type region, a p-type region and a mid gap region; a p-typesemiconductor device present in the p-type region having a p-type workfunction gate structure comprised of a first high-k gate dielectric, afirst metal containing buffer layer present on the first high-k gatedielectric, and a first titanium nitride layer having a first thicknesspresent on the first metal containing buffer layer; a mid gapsemiconductor device present in the mid gap region of the semiconductorsubstrate having a mid gap gate structure comprised of a second high-kgate dielectric, a second metal containing buffer layer present on thesecond high-k gate dielectric, and a second titanium nitride layerhaving a second thickness that is less than the first thickness presenton the second metal containing buffer layer; wherein the mid gapsemiconductor device has a gate work function ranging from 4.5 eV to 4.6eV, and an n-type semiconductor device present in the n-type regionhaving an n-type work function gate structure comprised of a thirdhigh-k gate dielectric present on a channel region of the n-typesemiconductor device, a third metal containing buffer layer on the thirdhigh-k gate dielectric, and a third titanium nitride layer present onthe third metal containing buffer layer having a third thickness lessthan the second thickness.
 12. The electrical device of claim 11,wherein the p-type semiconductor device further comprises a first gateconductor contact present on the first titanium nitride layer, the midgap semiconductor device further comprises a second gate conductorcontact present on the second titanium nitride layer, and the n-typesemiconductor device further comprises a third gate conductor contactpresent on the third titanium nitride layer.
 13. The electrical deviceof claim 11, wherein the p-type semiconductor device is a p-type FinFET,the mid gap semiconductor device is a mid gap FinFET, and the n-typesemiconductor device is an n-type FinFET, or the p-type semiconductordevice is a planar p-type FET, the mid gap semiconductor device is aplanar mid gap FET, and the n-type semiconductor device is planar n-typeFET.
 14. The electrical device of claim 11, wherein at least one of thefirst metal containing buffer layer, the second metal containing bufferlayer and the third metal containing buffer layer comprises tantalumnitride (TaN).
 15. A method of forming a semiconductor devicecomprising: providing a semiconductor substrate having an n-type region,a p-type region and a mid gap region; forming a p-type semiconductordevice in the p-type region having a p-type work function gate structurecomprised of a first high-k gate dielectric, a first metal containingbuffer layer present on the first high-k gate dielectric, and a firsttitanium nitride layer having a first thickness present on the firstmetal containing buffer layer; forming a mid gap semiconductor device inthe mid gap region of the semiconductor substrate having a mid gap gatestructure comprised of a second high-k gate dielectric, a second metalcontaining buffer layer present on the second high-k gate dielectric,and a second titanium nitride layer having a second thickness that isless than the first thickness present on the second metal containingbuffer layer; wherein the mid gap semiconductor device has a gate workfunction ranging from 4.5 eV to 4.6 eV, and forming an n-typesemiconductor device in the n-type region having an n-type work functiongate structure comprised of a third high-k gate dielectric; a thirdmetal containing buffer layer on the third high-k gate dielectric, and an-type gate conductor contact present on the third metal containingbuffer layer.
 16. The method of claim 15, wherein the p-typesemiconductor device further comprises a p-type gate conductor contactpresent on the first titanium nitride layer, and the mid gapsemiconductor device further comprises a mid gap gate conductor contactpresent on the second titanium nitride layer.
 17. The method of claim15, wherein the n-type gate conductor contact is in direct contact withthe third metal containing buffer layer.
 18. The method claim 15 furthercomprising a third titanium nitride layer having a third thickness thatis less than the second thickness, the third titanium nitride layerpresent on the third metal containing buffer layer, wherein the n-typegate conductor contact is in direct contact with the third titaniumnitride layer.
 19. The method of claim 15, wherein forming the firsttitanium nitride layer and the second titanium nitride layer comprises:depositing a single titanium nitride material layer having said firstthickness for the first titanium nitride layer on the first metalcontaining buffer layer over a channel region of the p-typesemiconductor device, on the second metal containing buffer layer over achannel region of the mid gap semiconductor device and on the thirdmetal containing buffer layer over a channel region of the n-typesemiconductor device; forming a block mask over the first titaniumnitride layer on the first metal containing buffer layer over thechannel region of the p-type semiconductor device; removing the singletitanium nitride material layer having said first thickness from the midgap region and the n-type region with an etch process that is selectiveto the second metal containing buffer layer and the third metalcontaining buffer layer; forming block masks over the p-type region andthe n-type region; and forming the second titanium nitride layer havingthe second thickness on the second metal containing buffer layer in themid gap region of the substrate.
 20. The method of claim 15, wherein thep-type semiconductor device is a p-type FinFET, the mid gapsemiconductor device is a mid gap FinFET, and the n-type semiconductordevice is an n-type FinFET, or the p-type semiconductor device is aplanar p-type FET, the mid gap semiconductor device is a planar mid gapFET, and the n-type semiconductor device is planar n-type FET.